Recent Advances in Magnesia Cement The document discusses recent advances in different types of magnesium cements including magnesium oxychloride cement (MOC), magnesium phosphate cement (MPC), magnesium ammonium phosphate cement (MAPC), magnesium potassium phosphate cement (MKPC), and magnesium oxysulfate cement (MOS). It provides information on the chemical reactions, properties, applications, and new developments for each type of magnesium cement. The document is presented by Claudio Manissero at a technology forum on October 9, 2015.

1. Recent Advances in
Magnesia Cement
Claudio Manissero, Premier CPG
SDC Technology Forum # 38
October 9th, 2015

2. Agenda
• Overview of magnesium cements
• Historical perspective
• MgO grades – product properties
• Magnesium Oxychloride Cement (MOC)
• Magnesium Phosphate Cement (MPC)
• Magnesium ammonium phosphate cement (MAPC)
• Magnesium potassium phosphate cement (MKPC)
• Magnesium Oxysulfate Cement (MOS)
• Applications

3. • Magnesium cements are so-called calcined cements
• Cements produced from calcined magnesium carbonate
rock (magnesite) and a cross-linking agent to form a
cementitious matrix.
• Water is needed for reaction and becomes part of the
matrix.
• Reactions are acid-base reactions.
• Reactions are exothermic. Heat generated dependent on
nature of crosslinking agent, speed of reaction and nature
of fillers.
Overview of Magnesium Cements

4. • Variations of magnesia cements predates invention of Portland
cement.
• Magnesium cement has been used for millennia in Germany,
Italy, France, Switzerland, India, China, Mexico, Latin America,
and New Zealand, among other countries.
• Original cements based on naturally occurring magnesia and
other metal oxides.
• Rediscovered and patented MOC by Stanislav Sorel in 1867
• Terrazzo floors of the 18th and 19th century were mainly MOC
based
• New interest in technology due to their durability and
environmentally friendly attributes.
Historical Perspective

5. • Ancient Rome – Prime
example is the Pantheon
• Source of material was
Magnesia, Italy
• Magnesia deposits
“calcined” by volcanic
activity in area.
• Widespread use in roman
buildings
Historical Perspective

6. • Other examples
• Sections of the Great Wall of
China
• Some Indian Stupas
Historical Perspective

7. • Raw material magnesium oxide (MgO) is derives from magnesite
(magnesium carbonate) rock or extracted from brine.
• In US only one operating mine at Gabbs, NV by Premier
Magnesia
Magnesium Oxide (MgO) grades
The Gabbs location
is a world-class
mine with 70 years
of proven ore
reserves and
probable reserves
over 120 years.

8. Magnesium Oxide (MgO) grades
Premier Magnesia Gabbs facility

9. Magnesium Oxide (MgO) grades
Martin Marietta Brine facility, Manistee, MI

10. Magnesium Oxide (MgO) grades
Light burned MgO
Burned at 700-
1000oC
Most reactive form
of MgO
Hard burned
MgO
Burned at 1000-
1500oC
Most reactivity
eliminated
Dead burned MgO
Burned at 1500-
2000oC
All reactivity
eliminated
Unburned
magnesite
mineral

11. Magnesium Oxide (MgO) grades
A variety of kilns are used to produce MgO
Rotary Kiln
Shaft Kiln
Inefficient Rotary Kilns or Shaft Kilns
can over burn or under burn material
which produces inconsistent product.

12. Magnesium Oxide (MgO) grades
Best available technology available are Multiple
Hearth Furnaces for the highest consistency
and highest quality product. Used to produce
light burned MgO
Equipment and process
used for calcining crucial
to production of
consistent product for
magnesium cements.

13. • Formed by reaction of MgO with magnesium chloride
(MgCl2) in the presence of water
• Grade of MgO usually light burned, high reactivity.
• The main bonding phases found in hardened MOC pastes
are Mg(OH)2 (magnesium hydroxide),
3Mg(OH)2•MgCl2•8H2O (3-form) and
5Mg(OH)2•MgCl2•8H2O (5-form). The 5-form exhibits
superior mechanical properties
• Increased amounts of water will decrease the ultimate
strength because the lower strength 3-form starts to
develop in competition with the 5-form.
Magnesium Oxychloride Cement (MOC)

14. Plastic Properties
• Neat MOC paste is very fluid and not suitable for casting. The addition of
fillers/aggregates and other components provides ability to control viscosity
and workability.
• Set time for neat MOC paste can vary from a few hours to 24-48 hours for a
fully formulated product.
• Curing is affected by temperature, air flow and humidity conditions.
• MOC tends to be thixotropic . Rheology can be controlled by selection of raw
materials, molar ratio and concentration of the magnesium chloride
solution.
• To improve flowability, high range water reducers used in OPC concrete are
applicable.
• Thorough mixing is necessary to “wet out” the mix.
• Since it is an acid/base reaction, MOC develops a significant heat of
hydration (e.g., 60-80 ̊C and temperatures above 100 ̊C have been reported).
Magnesium Oxychloride Cement (MOC)

15. Hardened Properties
• MOC develops high compressive strength within 48 hours (e.g., 8,000-
10,000 psi). Compressive strength gain occurs early during curing - 48-hour
strength will be at least 80% of ultimate strength.
• Flexural strength of MOC is low but can be significantly improved by the
addition of fibers. MOC is compatible with a wide variety of plastic, mineral
(such as basalt fibers) and organic fibers such as bagasse, wood fibers and
hemp.
• MOC is non-shrinking, abrasion and wear resistant, impact, indentation and
scratch resistant
• MOC is stable to heat and freeze-thaw cycles and does not require air
entrainment to improve durability.
• MOC has excellent thermal conductivity, low electrical conductivity, and
excellent bonding to a variety of substrates and additives.
• Excellent fire resistance properties
Magnesium Oxychloride Cement (MOC)

16. Issues/New Developments
• MOC is not stable in prolonged contact with water and can result in the
leaching of magnesium chloride, with reversal of the reaction and loss in
strength.
• Over a period of time, atmospheric carbon dioxide reacts with magnesium
oxychloride to form a surface layer of Mg2(OH)ClCO3•3H2O. This layer slows
the leaching process.
• Additional leaching leads to the formation of hydromagnesite, which is
insoluble and results in maintenance of structural integrity.
• A variety of additives have been developed that will significantly slow down
or block water penetration during early ages, or expedite formation of
hydromagnesite.
• Materials used include: phosphates, fly ash, silica fume, alkali metal sulfates
and fatty acids.
Magnesium Oxychloride Cement (MOC)

17. Magnesium ammonium phosphate cement (MAPC)
• MAPC is formed by reaction of MgO with monoammonium dihydrogen
phosphate (NH4H2PO4), also referred to as ADP.
• A wide variety of insoluble ammonium and magnesium phosphate phases are
formed, but struvite (NH4MgPO4•6H2O) and dittmarite (NH4MgPO4•H2O) are
believed to be the main phases.
• The ratio of these phases is dictated by the speed of reaction, with dittmarite
being predominant at a fast rate and struvite being predominate at a slower
rate.
• At temperatures above 55 ̊C, struvite decomposes releasing water and ammonia
from its structure. The resulting material has an amorphous structure that
corresponds chemically to MgHPO4.
• ADP is added in excess to ensure full reaction and provide higher
compressive strength in the hardened concrete resulting in the excess ADP
being volatilized during curing.
• Due to a very fast rate of reaction, the MgO normally used is dead-burned.
• Retarders, normally borates, are used to achieve a manageable reaction time.
Magnesium Phosphate Cement (MPC)

18. Magnesium potassium phosphate cement (MKPC)
• MKPC is formed by reaction of MgO with monopotassium phosphate
(KH2PO4), referred to as MKP.
• Final reaction product is identified as magnesium potassium phosphate
hexahydrate (MgKPO4•6H2O)
• Various intermediate phases are formed during the reaction as the pH and
temperature vary during the reaction.
• Both increasing the molar ratio of magnesium to phosphate (M/P) and
decreasing the weight ratio of liquid to solid can accelerate the reaction rate.
• Due to a very fast rate of reaction, the MgO normally used is dead-burned.
• Retarders, normally borates, are used to achieve a manageable reaction time.
Magnesium Phosphate Cement (MPC)

19. Plastic Properties
• MPC cements are very fast setting materials with low flow characteristics.
• Both plastic and hardened properties are affected by the other components
of the mixture, the grade of MgO used, the ratios of MgO and phosphate,
and w/b ratio.
• Typical set times range between 2-15 minutes for initial set and up to 20-30
minutes for final set.
• The temperature at placement has a significant effect on set times, with
mixtures that normally set in 10-15 minutes at 20 ̊C (60 ̊F) setting in 5-8
minutes at 30 ̊C (86 ̊F). Cooling the mixture water helps control set times.
• MPC mixtures are thixotropic in nature and therefore do not flow well. When
shear force or vibration is applied, MPC flows easily.
• Since it is an acid/base reaction, MPC develops a significant heat of hydration
(up to 80 ̊C). Temperature evolution is significantly decreased when fillers
are added to the paste, creating mixtures that are safe to handle and place.
Magnesium Phosphate Cement (MPC)

20. Hardened Properties
• MPC mixtures develop high compressive strength within the range of
5,000-10,000 psi (35-70 MPa). MPC does not lose strength over time
under normal exposure conditions.
• A number of factors affect strength development, with the largest effect
observed being the ratios of reactants (M/P), w/b ratio, amount of
retarders used, and materials added as fillers/aggregates to the binder.
• Flexural strengths of 600-2,000 psi (4-14 MPa) have been reported with
little effect on strength due to reactant ratios. Addition of fibers
improves flexural strength.
• MKP exhibit minimal shrinkage, excellent freeze-thaw resistance, and
very low permeability. It also has low coefficient of thermal expansion,
excellent corrosion protection, and high abrasive resistance. Immersion
in magnesium sulfate solution increases strength.
• MKP exhibits good adhesion to weathered concrete substrates
Magnesium Phosphate Cement (MPC)

21. Issues/New Developments
• Due to sensitivity of reaction, significant variability has been observed
with MPC mixes. The variability is due to variability in dead burn MgO.
• Recent advances have been made to utilize more reactive, but more
consistent light burn MgO.
• Changes in reagent ratios and development of alternative retarders as
well as changes in fillers have resulted in mixes that have set times
similar to “traditional” MPC formulations with only slight loss in
strength.
• Recent developments have been reported on corrosion and fire
protection coatings based on MKPC.
• Use of additives and fibers have resulted in formulations useful for
flexural strengthening of concrete structures utilizing glass mesh (low pH
of mixture prevents ASR reaction).
Magnesium Phosphate Cement (MPC)

22. • MOS is formed by reaction of MgO with magnesium sulfate in the
presence of water. The cement is a homologue of MOC.
• Grade of MgO usually light burned, high reactivity. The magnesium
sulfate salt used is the heptahydrate salt, also known as Epsom salt.
• There are four main bonding phases formed during reaction:
5Mg(OH)2•MgSO4•3H2O (5-form), 3Mg(OH)2•MgSO4•8H2O (3-
form), Mg(OH)2•MgSO4•5H2O, and Mg(OH)2•2MgSO4•3H2O.
• Only the 3-form and the 5-form are stable at room temperature. The
3-phase is the phase that provides compressive strength.
• Like MOC, MOS has low water resistance and loses strength over time
when immersed in water due to a reversal of the reaction.
Magnesium Oxysulfate Cement (MOS)

23. Plastic Properties
• MOS, like MOC, is very fluid and not suitable for casting. The addition
of fillers/aggregates and other components provides ability to control
viscosity and workability.
• Vicat initial set times of 30 minutes and final set time of 130 minutes
were reported using a stoichiometric mixture of components to
maximize formation of the 5-form
• Curing of MOS is less effected by weather conditions of humidity,
temperature and wind than MOC.
• Rheology of MOC can be controlled by selection of raw materials,
molar ratio and the nature of fillers. In general MOS is less thixotropic
and more fluid than MOC. Fly ash has been reported to improve
rheology (at the expense of compressive strength)
• Since it is an acid/base reaction, MOS develops a significant heat of
hydration which has been shows to result in thermal cracking.
Magnesium Oxysulfate Cement (MOS)

24. Hardened Properties
• MOS has been reported to reach 3000-5000 psi in 1 day and up to
10000 psi at 28 days.
• A number of factors affect strength development, with the largest
effect observed being the ratios of reactants (M/P). Addition of
fly ash results in significant strength loss.
• Flexural strength has been reported to be 500 psi in 7 days.
• MOS has better volumetric stability, less shrinkage, better bond to
substrate and lower corrosivity under a significantly wider range
of weather conditions than MOC.
• With traditional formulations MOS has worse water resistivity
than MOC limiting its applications.
Magnesium Oxysulfate Cement (MOS)

25. Issues/New Developments
• Due to water sensitivity of reaction and relatively slow reaction and
limited strength gain, MOS has received limited attention over the other
magnesium cements.
• Recent work and advances have addressed the issues with MOS
• Addition of citric acid significantly improves compressive strength to
12000-15000 psi
• Addition of dolomite, magnesite or other fillers at a level of 40-60% of
binder can absorb some of the heat and reduce the chances for thermal
cracking
• Flexural strength can be doubled by addition of combination of citrate and
sodium silicate in 1:1 proportions.
• These combinations significantly improved water resistance.
• Addition of sodium bicarbonate significantly improved water resistance.
Magnesium Oxysulfate Cement (MOS)

26. MOS Applications
• Most widespread
application of MOS is for
wallboard, backer slats,
ceiling tiles, decorative
panels, firewalls, SIP board
systems
• Still considerable use in
flooring applications by
development of suitable
coatings and improved
water resistance additives.
• Fire proofing coatings.
Applications

27. MPC Applications
• Fast patching mixes for
bridges/roads
• Hazardous waste/nuclear
waste encapsulation
• Shotcrete applications
• Mortar for carbon fiber
reinforced applications
• Permafrost, low
temperature applications
• Corrosion protective
overlays, coatings
• Fire proofing coatings.
Applications